Manual strapping tools have been widely used for many years to apply steel straps or polymeric straps, such as polyester or polypropylene straps, in tensioned loops around packages of diverse types. Some of these strapping tools employ metal seals, which are crimped onto overlapped layers of such steel or polymeric straps. Others punch interlockable keys into overlapped layers of steel straps. Others produce friction welds between overlapped layers of polymeric straps.
As an example, Cheung U.S. Pat. No. 3,998,429 discloses a manual strapping tool having a tension-sensing handle, which is used to actuate a tensioning mechanism via a shaft driven rotatably by the handle. The handle is articulate and comprises a drive lever, which is coupled to the shaft via a ratchet drive, and a handle lever, which is mounted pivotally to the drive lever. The handle lever is biased against the drive lever by a biasing spring, which is adjustable via an adjusting screw.
In the manual strapping tool disclosed in the Cheung patent noted above, pivotal movement of the handle in one rotational direction tensions a strap. When sufficient tension has been imparted to the strap, the biasing spring is compressed and the handle lever pivots on the drive lever, until an arm on the handle lever engages a fixed set of stop teeth. When the arm engages such teeth, the drive lever cannot be further pivoted in the rotational direction noted above, except in small increments in a manner explained in such patent.
In a tensioning mechanism for a strapping tool, two additional features would be highly desirable. Specifically, it would be highly desirable if tension limits could be user-adjusted within a separately adjustable range. Also, it would be highly desirable if the handle of the tensioning mechanism could not be further pivoted in small increments after a tension limit had been reached.